1. Technical Field
The present invention relates to a thin film electrode ceramic substrate and a method for manufacturing the same.
2. Description of the Related Art
Recently, electronic components used in a mobile communication field are increasingly required to be small-sized, integrated, modularized, and allow high frequency, due to the technical advancement in mobile communication. In order to satisfy these required techniques, high-temperature co-fired ceramic (HTCC) or low-temperature co-fired ceramic (LTCC) multilayer substrates are widely used.
A demand for ceramic substrate in which a thin film electrode pattern, without using the existing electrode printing method, is applied onto a surface of a highly integrated multilayer substrate for a probe card, which tests a high-frequency module, a microwave connector, a cable assembly, a semiconductor chip, and the like, for current mobile communication, is increasing. The reason is that the thin film electrode pattern enables fine patterns to be formed on a surface of the ceramic substrate, as compared with the existing printing electrode pattern, and a thickness of the plating layer is increased.
An HTCC multilayer substrate is manufactured by thermal treatment at a temperature of 1500° C. or higher. As for materials for the HTCC ceramic multilayer substrate, 94% or more of alumina is used as a main raw material and a small amount of SiO2 is used as an additive. As a material for the electrode pattern, tungsten (W) that can be high-temperature fired is mainly used.
The HTCC ceramic multilayer substrate has excellent mechanical strength and chemical-resistant property, and thus is widely used as a highly integrated package, by forming thin film electrode patterns on a substrate surface. However, the high-temperature fired tungsten (W) electrode pattern has lower electrical conductivity than silver (Ag) or copper (Cu), resulting in deteriorating high frequency characteristics, and has about 2 times higher thermal expansion coefficient than a silicon semiconductor device, resulting in raising problems in an application field where matching of the thermal expansion coefficient is requested.
While, the LTCC ceramic multilayer substrate is manufactured by thermal treatment at a temperature of 900° C. or lower. In order to use the LTCC ceramic multilayer substrate at a low temperature of 900° C. or less, a large amount of SiO2 having a low melting point is used and a relatively small amount of alumina is used. Silver (Ag) or copper (Cu) can be used as a material for electrode patterns because a firing temperature is 900° C. or less, and thus, resistors, inductors, and condensers, which are passive elements, are embedded inside the substrate. Therefore, the LTCC ceramic multilayer substrate is widely used to make electronic components be small-sized, integrated, modularized, and allow high frequency.
However, since the LTCC ceramic multilayer substrate contains much SiO2, a substrate surface, in which SiO2 is contained, is easily etched during an etching process using a strong acid type chemical material such as hydrofluoric acid (HF) or a strong base type chemical material such as potassium hydroxide (KOH), and thereby to reduce the binding strength of thin film electrode patterns formed on a surface of the LTCC multilayer substrate.
FIG. 1 shows a procedure of forming thin film electrode patterns on a surface of a ceramic multilayer substrate according to the related art.
First, fine thin film electrode layers 11 and 12 are formed on a ceramic multilayer substrate 10. Then, a photosensitive protective layer 13 is formed on the fine thin film electrode layers 11 and 12. Then, the photosensitive protective layer 13 is exposed and developed so as to embody electrode patterns to be formed on a surface of the ceramic multilayer substrate 10. Then, a plating layer 14 is formed in a part in which a portion of the photosensitive protective layer 13 is removed by development. Then, the photosensitive protective layer 13 is removed. Finally, the thin film electrode layers 11 and 12 are sequentially etched to leave electrode patterns 11 and 12 and a plating pattern 14 on the surface of the final multilayer ceramic substrate 10.
The thin film electrode layers 11 and 12 are made of, for example, a titanium (Ti) electrode 11 and a copper (Cu) electrode 12. However, a problem occurs in etching the titanium (Ti) electrode 11 formed on the multilayer ceramic substrate 10. Generally, an etchant used at the time of etching titanium contains a strong acid type chemical material such as hydrofluoric acid (HF) or a strong base type chemical material such as potassium hydroxide (KOH).
For this reason, as shown in FIG. 2, when the Ti electrode 11 is etched, the surface of the ceramic multilayer substrate, in which a large amount of SiO2 is contained, is easily etched. Furthermore, undercut occurs between the surface of the substrate 10 and the titanium electrode 11 and the copper electrode 12 and the titanium electrode 11 (see, “A”), and thus, a thin film electrode pattern is difficult to form, and the binding strength of the thin film electrode pattern to the surface of the substrate is reduced even though the thin film electrode pattern is formed.